During the semiconductor manufacturing process, a wafer-transportation apparatus transports the wafer to at least one process chamber for implementing a certain manufacturing process. Generally, the wafer transportation apparatus includes a robot arm, and a paddle or a fork at the end of the robot arm to carry the wafer. The robot arm and the fork are driven by a motor with some belts, screws, cables and pulleys. In order to detect the movements of the wafer transportation apparatus, some encoders are arranged on the motor or the screws for detecting. However, there are still challenges in positioning and adjusting the movements of the wafer transportation apparatus.
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the embodiments and are not necessarily drawn to scale.